In the Nexus Repository Manager web browser, select Browse and make note of the format of the repository that you want to upload files to.
Lets say you want to upload files to a repository that is using the Maven format. You can either upload an individual file, such as foo.txt, or an archive that contains multiple files, such as foo.zip.
In this example, foo.zip will be uploaded to the repository named my-repo.
Now, when viewing the repository, you should the directory structure you created (base > core > 1.0) and below the third folder will be a .zip file. In this example, the name of the file is core-1.0.zip, and core-1.0.zip will contain whatever files were in the foo.zip archive.
You could then use the curl command to download files in Nexus, like this.
curl -u "username:password" -o "/tmp/foo.zip" "http://nexus.example.com/repository/my-repo/base/core/1.0/core-1.0.zip"